1. Technical Field of the Invention
The present invention relates generally to a timepiece having a reflective and flexible display, and specifically to the mechanical solutions involved in implementing such a watch and to the multiple environments in which such a watch could be implemented.
2. Description of Prior Art
Watches come in a variety of shapes and sizes. The watch display is usually either mechanical with at least two hands that sweep around a marked dial or a liquid crystal display. In either case, one common constraint for prior art watches is the rigidity of the display. It is common for the display to have a metal casing and either a glass or hard plastic crystal.
FIG. 1A illustrates a standard prior art watch 10. The watch has a thick case 12 that contains the time keeping mechanism. The case can be anywhere from a few millimeters thick to well over a centimeter. The case can be made of metal or a hard plastic; but in either case, it must be rigid to protect the time keeping mechanism. Likewise, FIG. 1B illustrates a generic digital watch 20. The watch also has a display. In many instances the display is a liquid crystal display (LCD) 22. An LCD display provides several advantages including generally low power requirements. The LCD is a reflective display. In other words, selected segments of the LCD display are biased to either a black or a gray state. The gray segments are approximately 15-25% reflective; so approximately one sixth to one quarter of the incident light produces either light or dark segments in the shape of numbers or letters. Ambient or supplemental light reflects off of the segments and the user can determine the time or date. LCD displays must also incorporate a hard display cover
A need exists for a flexible display for watches. A flexible display would allow for a number of significant advancements in the design and mechanical implementation of watches. Despite much effort directed to developing highly flexible, reflective display media, there are relatively few examples of displays formed on semi-flexible substrates, and these examples have found only moderate success. For example, plastic-based liquid crystal displays, including twisted nematic (TN), supertwisted nematic (STN), polymer dispersed liquid crystal (PDLC), and bistable cholesteric liquid crystals have been developed. Nevertheless, problems remain with liquid crystal alignment in TN and STN displays, cholesteric displays are sensitive to changes in their cell gap, and local stress can cause changes in the scattering or absorbance of PDLC and cholesteric films. As such, only moderate flexibility can be achieved with these displays.
Emissive electroluminescent films and organic light emitting diode films can be deposited on flexible substrates to create flexible displays. However, these devices require continuous power consumption for operation, and thus are not practical for many applications.
The concept of electronic ink, or e-ink, is disclosed in U.S. Pat. No. 6,118,426, owned by E-Ink Corp. of Cambridge Mass. An encapsulated electrophoretic display can be constructed so that the optical state of the display is stable for some length of time. When the display has two states that are stable in this manner, the display is said to be bistable. If more than two states of the display are stable, then the display can be said to be multistable. The term bistable indicates a display in which any optical state remains fixed once the addressing voltage is removed. The definition of a bistable state depends on the application for the display. A slowly-decaying optical state can be effectively bistable if the optical state is substantially unchanged over the required viewing time. For example, in a display that is updated every few minutes, a display image which is stable for hours or days is effectively bistable for that application. The term bistable also indicates a display with an optical state sufficiently long-lived as to be effectively bistable for the application in mind. Alternatively, it is possible to construct encapsulated electrophoretic displays in which the image decays quickly once the addressing voltage to the display is removed (i.e., the display is not bistable or multistable). Whether or not an encapsulated electrophoretic display is bistable, and its degree of bistability, can be controlled through appropriate chemical modification of the electrophoretic particles, the suspending fluid, the capsule, and binder materials.
An encapsulated electrophoretic display may take many forms. The display may comprise capsules dispersed in a binder. The capsules may be of any size or shape. The capsules may, for example, be spherical and may have diameters in the millimeter range or the micron range, but is preferably from ten to a few hundred microns. Particles may be encapsulated in the capsules. The particles may be two or more different types of particles. The particles may be colored, luminescent, light-absorbing or transparent, for example. The particles may include neat pigments, dyed (laked) pigments or pigment/polymer composites, for example. The display may further comprise a suspending fluid in which the particles are dispersed.
Referring to FIG. 2A, a display 30 is created by printing a first conductive coating 32 on a substrate 34, printing an electronic ink 36 on the first conductive coating 32, and printing a second conductive coating 38 on the electronic ink 36. Conductive coatings 32, 38 may be Indium Tin Oxide (ITO) or some other suitable conductive material. The conductive layers 32, 38 may be applied from a vaporous phase, by electrolytic reaction, or deposition from a dispersed state such as spray droplets or dispersions in liquids. Conductive coatings 32, 38 do not need to be the same conductive material. For example, the substrate 34 is a polyester sheet having a thickness of about 4 mil, and the first conductive coating 32 is a transparent conductive coating such as ITO or a transparent polyaniline. The second conductive coating 38 may be an opaque conductive coating, such as a patterned graphite layer. Alternatively, the second conductive coating 38 can be polymeric. The polymer can be intrinsically conductive or can be a polymer carrier with a metal conductor such as a silver-doped polyester or a silver-doped vinyl resin. Conductive polymers suitable for use as the second electrode include, for example, polyaniline, polypyrole, polythiophene, polyphenylenevinylene, and their derivatives. These organic materials can be colloidally dispersed or dissolved in a suitable solvent before coating. Of course, for the pixel orientation to be visible, it is preferable that the second conductive coating 38 be transparent.
The display 30 can also be created by printing a first conductive coating 32 on a first substrate 34, printing an electronic ink 36 on the first conductive coating 32, printing a second conductive coating 38 on a second substrate 34xe2x80x2 (not shown), and configuring the substrates 34, 34xe2x80x2 such that the second conductive coating 38 is in electrical communication with the electronic ink 36.
The electronic ink 36 comprises a plurality of capsules. The capsules, for example, may have an average diameter on the order of about 100 microns. Capsules this small allow significant bending of the display substrate without permanent deformation or rupture of the capsules themselves. The optical appearance of the encapsulated medium itself is more or less unaffected by the curvature of these capsules. FIG. 2B illustrates one example of the display media 40. A microcapsule or cell 42, filled with a plurality of metal sol 46 and a clear fluid 44. Metal sol 46 is particles, which are smaller than a wavelength of light. In one detailed embodiment, the metal sol 46 comprises gold sol. When an electric field is applied across the microcapsule or cell 42, sol particles 46 agglomerate and scatter light. When the applied electric field is reduced to below a certain level, Brownian motion causes the sol particles 46 to redistribute, and the display media 40 appears clear from the clear fluid 44.
One of the benefits of using printing methods to fabricate displays is eliminating the need for vacuum-sputtered ITO by using coatable conductive materials. The replacement of vacuum-sputtered ITO with a printed conductive coating is beneficial in several ways. The printed conductor can be coated thinly, allowing for high optical transmission and low first-surface reflection. For example, total transmission can range from about 80% to about 95%. In addition, the printed conductive coating is significantly less expensive than vacuum-sputtered ITO. Another advantage of the encapsulated electrophoretic display medium is that relatively poor conductors can be used as lead lines to address a display element.
The flexible, inexpensive display described above is useful in numerous applications. For example, these flexible displays can be used in applications where paper is currently the display medium of choice. Alternatively, the displays can be made into disposable displays. The displays can be tightly rolled or bent double. In other embodiments, the displays can be placed onto or incorporated into highly flexible plastic substrates, fabric, or paper. Since the displays can be rolled and bent without sustaining damage, they form large-area displays that are highly portable. Since these displays can be printed on plastics they can be lightweight. In addition, the printable, encapsulated electrophoretic display can maintain the other desirable features of electrophoretic displays, including high reflectance, bistability, and low power consumption.
One alternative to E-ink""s electrophoretic display is a gyricon display. Gyricon displays are based on a different principal, namely the use of sphere having two different colored hemispheres, such as a white side and a dark side. Xerox has largely developed this technology, as demonstrated by its U.S. Pat. No. 5,808,783. In the ""783 patent a gyricon or twisting-ball display is disclosed having reflectance characteristics comparing favorably with those of white paper. The display is based on a material made up of optically anisotropic particles, such as bichromal balls, disposed in a substrate having a surface. The particles situated closest to the substrate surface form substantially a single layer. Each particle in the layer has a center point, no particle in the layer being disposed entirely behind the center point of any nearest neighboring particle in the layer with respect to the substrate surface. Each particle in the layer has a projected area with respect to the substrate surface. Particles of the set are sufficiently closely packed with respect to one another in the layer that the union of their projected areas exceeds two-thirds of the area of the substrate surface. A rotatable disposition of each particle is achievable while the particle is thus disposed in the substrate; for example, the particles can already be rotatable in the substrate, or can be rendered rotatable in the substrate by a nondestructive operation. In particular, the particles can be situated in an elastomer substrate that is expanded by application of a fluid thereto so as to render the particles rotatable therein. A particle, when in its rotatable disposition, is not attached to the substrate. A reflective-mode display apparatus can be constructed from a piece of the material together with a mechanism (e.g., addressing electrodes) for facilitating rotation of at least one of the particles.
FIG. 2C provides a more detailed side view of a gyricon display 50 of the invention in a specific embodiment. In display 50, bichromal balls 52 are placed as close to one another as possible in a monolayer in elastomer substrate 54. Substrate 54 is swelled by a dielectric fluid (not shown) creating cavities 56 in which the balls 52 are free to rotate. The cavities 56 are made as small as possible with respect to balls 52, so that the balls nearly fill the cavities. Also, cavities 52 are placed as close to one another as possible, so that the cavity walls are as thin as possible. Preferably, balls 52 are of uniform diameter and situated at a uniform distance from upper surface 58.
Balls 52 are electrically dipolar in the presence of the dielectric fluid and so are subject to rotation upon application of an electric field, as by matrix-addressable electrodes 60, 62. The electrode 60 closest to upper surface 58 is preferably transparent. An observer sees an image formed by the black and white pattern of the balls 52 as rotated to expose their black or white hemispheres to the upper surface 58 of substrate 54
A monolayer gyricon display according to the invention has advantages in addition to improved reflectance. The operating voltage needed for such a display is less than the voltage needed for a conventional thick gyricon display. This is because the rotation of gyricon balls under the influence of an electric field depends on the field strength. Electric field is the derivative of voltage with respect to distance (for example, in the simple case of a parallel plate capacitor, E=V/d). Thus a given electric field strength can be achieved with a lower applied voltage, other things being equal, by reducing the distance over which the voltage is applied. Accordingly, by using the thinnest configuration possible, the operating voltage of the gyricon display is minimized. A lower operating voltage has many advantages, including lower power consumption, less expensive drive electronics, and increased user safety.
Despite the promise of e-ink and gyricon displays, neither technology has achieved any level of commercial implementation. A need exists for translating these technologies into useful displays in the field of watches.
The present invention addresses many of the shortcomings of the prior art watch technology. Specifically, a watch that embodies the present invention is highly flexible and uses addressable reflective display technology such as electronic ink or gyricons. This allows a watch display that can be flexible. Further, the display can be shaped into a variety of interesting and novel designs that cannot be accomplished using prior art displays.
The flexibility of the display also allows for the novel placement of the watch display. For example, the display can be placed onto a shoe, allowing a runner to see the time without having to move his arm into a viewing position. The watch display could also be placed into a wallet, or on a purse or belt. Any flexible garment or accessory could now incorporate a watch. The patent discloses enclosures to provide for a flexible product, but limit flexibility to prevent damage to the display in usage.
The use of an electrophoretic display or gyricon display is also aided by new sealing technologies that allow the display to be incorporated into high wear, high flex items.